This is a very personal list and may not work for everybody, but if you plan to write a novel here are 10 things that you may want to do:
1. Figure out why you want to write it. If it’s just that everybody else is doing it and you have some free time on your hands, get a dog instead.
2. Think up a central subject and work on a rough plot. Nothing too elaborate, just something to start working with.
3. Get acquainted with your main characters; don't you even think of writing a line before you do. Spend time placing them in the environment that fits your plot (if it’s a historic novel, for instance, dress them up accordingly) and just play with them in your head. See what they look like, how they move, talk, behave, and let them develop until you are satisfied with them.
4. Take some notes. From this point on, details pile up and you may forget an important one. Quick bullet-point notes will help you later on.
5. Research. Now that you have an idea of the set-up and of the main characters involved you want to learn as much as possible about them. If the location where the action takes place is real and specific, read about it, study maps, look for pictures of it. In other words, get immersed in it. If your plot involves real historic characters, read everything you can get your hands on about them, until you feel that you know them intimately.
6. Take a break. Read a book by one of your favorite authors. Make sure to pick one that has no relevance to your specific plot.
7. Re-read Strunk, White & Kalman’s The Elements of Style, cover to cover. It doesn't matter that you have already read it 15 times before. Read it again.
8. Find a quiet room in the house to work in with the door closed. Never mind that there is nobody else around. Close the door to the outside world.
9. Write whenever you feel like it. You must have read the usual advice about having regular writing hours and sitting down every day at the same time to write a given number of words. That works very well if you have to write an instruction manual for a washing machine. For a novel you must follow your obsession and write whenever you feel like it. It is not uncommon for me to jump out of bed at 2 am to jot down a few paragraphs that have occurred to me in the shower and keep nagging me. Write 15 minutes before going to work or 5 straight hours when you’re home from your day job. Whatever. Write on the train, at the airport, at the beach. Forget writing schedules. If you’re not obsessed, write for the washing machine company.
10. Close the door and write Chapter 1. Don't plan it (if you followed the above advice you have done all the planning you need), just let it happen. Reading that chapter will tell you if there is any point in writing on.